Cautions for rubber accelerators selection and use

- Dec 21, 2018-

Cautions for accelerators selection and use 
①Rubber types:Different rubbers adopt different curing systems, and different vulcanization systems naturally include different types of accelerators to ensure the matching. 
②Scorch performance:The accelerator determines the scorch time of the compound (the time before the heat vulcanization begins). Therefore, the accelerator should make the compound have a considerable scorch time, which plays an important role in the operation safety, the fluidity of the initial rubber and the adhesive force of the fabric in the process of mixing, calendering, extrusion or injection. Especially in recent years, in order to improve production efficiency, processing conditions become much stricter, the anti-scorch performance requirements of the rubber compound is also higher and higher. But the excessive long burning time will lead to the increase of the total vulcanization time, which is not only detrimental to the improvement of labor efficiency, but also to the deformation of non mold curing products in the process of vulcanization will also have adverse effects. The scorch resistance of the accelerator is directly related to its critical temperature ( the temperature at which the accelerator acts on the curing process). Under this temperature, the accelerator activity is not significant; above this temperature, the accelerator is activated and its sulfidation is fully brought into play. Unfortunately, most accelerators have not yet measured this temperature.When a plurality of accelerators are used in combination, the activity of some accelerators is inhibited, and some accelerators exhibit greater activity even below their critical temperature. 
③ Vulcanization flatness:Accelerators should allow the rubber to have a broad flat curve during the optimum curing process. In other words, the properties of the vulcanizates should not change significantly during this period, which is particularly important for rubber thick and solid products.Rubber is a poor conductor of heat, the surface and internal heating of vulcanized rubber is not consistent, wide vulcanization flatness is to avoid over-sulfur and ensure that the product parts of vulcanization uniform. 
④Effect on properties of rubber compound and vulcanizate:The accelerator participates in the formation of rubber net structure during vulcanization, which is directly related to the structure of vulcanized rubber, that is to say, its physical and mechanical properties and aging properties. Some accelerators soften the rubber compound, increase the plasticity of the rubber compound, and change the process ability of the rubber compound. Therefore, it is necessary to choose accelerators to understand these properties. 
⑤Dispersivity:The accelerator with poor dispersing property in the rubber compound not only needs longer mixing time, increases the power consumption of the equipment, but also tends to cause uneven vulcanization due to uneven mixing. For some difficult dispersing accelerator, it can be used as rubber compound.
⑥Pollution and coloring:Some accelerators make rubber products colored because of their different colors.And some are discolored by chemical or sunlight exposure which can not be used as white or bright colored products. In addition, some promoters can contaminate other substances by contact migration.  
⑦Water solubility:For the production of latex products, the use of water-soluble accelerator is more convenient. 
⑧Toxicity:Most of the accelerators currently used are non-toxic.But some promoters have a bad smell and individually some are toxic,which cannot be used in medical products and food-contact rubber products.The use of toxic accelerators should be protected during operation.
⑨The combination of accelerators:Each accelerator has its own characteristics. In order to meet the good performance of the rubber in the process of operation and to make the vulcanizate have excellent physical and chemical properties, several accelerators can be used together to complement each other. 
⑩Factors such as interaction with other ingredients and cost also need to be considered.